#include <string.h>
#include <stdint.h>
#include <limits.h>

#define ALIGN (sizeof(size_t)-1)
#define ONES ((size_t)-1/UCHAR_MAX)
#define HIGHS (ONES * (UCHAR_MAX/2+1))
#define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)

void *memccpy(void *restrict dest, const void *restrict src, int c, size_t n)
{
    unsigned char *d = dest;
    const unsigned char *s = src;

    c = (unsigned char)c;
#ifdef __GNUC__
    typedef size_t __attribute__((__may_alias__)) word;
    word *wd;
    const word *ws;
    if (((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) {
        for (; ((uintptr_t)s & ALIGN) && n && (*d=*s)!=c; n--, s++, d++);
        if ((uintptr_t)s & ALIGN) goto tail;
        size_t k = ONES * c;
        wd=(void *)d; ws=(const void *)s;
        for (; n>=sizeof(size_t) && !HASZERO(*ws^k);
               n-=sizeof(size_t), ws++, wd++) *wd = *ws;
        d=(void *)wd; s=(const void *)ws;
    }
#endif
    for (; n && (*d=*s)!=c; n--, s++, d++);
tail:
    if (n) return d+1;
    return 0;
}
